Hydraulically powered pump having a precompression function

ABSTRACT

An hydraulically powered multiplex pump having at least three pumping units, each operable in a cycle including suction, precompression and discharge phases, with the cycles being out of phase with one another, whereby simultaneous performance of these functions results in a substantially constant pressure and flow of both the pumped fluid and the power fluid. Separate power and cycle control circuits, which may employ different fluids, are provided. Control valve assemblies, each including two sleeve valves communicating with a common chamber, are operated by the control circuit fluid to condition power circuit flow for the various phases of the pumping cycle. The power end of the pumping units includes power cylinders which may be fluid interconnected at their rod ends so that operations in each power cylinder affect functions in the other chambers, and provision is made for automatic correction of errors in stroke length.

United States Patent Cole [451 Mar.21,19'72 [54] HYDRAULICALLY POWERED PUMP HAVING A PRECOMPRESSION FUNCTION I 72 inventor: Clinton w. Cole, Duncan, Okla.

[73] Assignee: Halliburton Company, Duncan, Okla.

[22] Filed: Dec. 19, 1969 [21] Appl. No.: 886,687

R25,568 5/1964 Sherrod ..4l7/90OX Primary ExaminerRobert M. Walker Attorney-Burns, Deane, Swecker & Mathis and John H. Tregoning [5 7] ABSTRACT An hydraulically powered multiplex pump having at least three pumping units, each operable in a cycle including suction, precompression and discharge phases, with the cycles being out of phase with one another, whereby simultaneous performance of these functions results in a substantially constant pressure and flow of both the pumped fluid and the power fluid. Separate power and cycle control circuits, which may employ different fluids, are provided. Control valve assemblies, each including two sleeve valves communicating with a common chamber, are operated by the control circuit fluid to condition power circuit flow for the various phases of the pumping cycle. The power end of the pumping units includes power cylinders which may be fluid interconnected at their rod ends so that operations in each power cylinder affect functions in the other chambers, and provision is made for automatic correction of errors in stroke length.

21 Claims, 18 Drawing Figures Patented March 21, 1972 16 Sheets-Sheet 2 lI-bl ZI-bl FIG.3

Patented March 21, 1972 16 Sheets-Sheet 5 FIGA Patented arch 21, 1972 l6 Shams-Sheet 4 Patented March 21, 1972 l6 Shams-$11901: 5

Patented March 21, 1912 v mamas 16 Sheets-Sheet 6 Patented March 21, 1972 16 Sheets-Sheet 7 Patented March 21, 1972 16 Sheets-Sheet 8 I ,TABLE A| VALVE -CONDIT CYLINDERFUNCTION II c 5 l0 0 #1 5 a IPR c 21 0 g 20 c #2 g A Q Q 2m c 29? 31 c I g 30 c #3 5g 3PR 0 Patented March 21, 1972 3,650,638

16 Shams-Sheet 10 TABLE A3 common 394 TRIPPED I A PRESSURIZED :I'FF'Efi/j Patented March 21, 1972 16 Sheets-Sheet l2 FIG.9 B2

ID 8 IPR AFFECTED OPERATION VALVES OPENED CLOSED OPENED CLOSED VALVE CONDITION PRESSURIZED TANKED TANKED VALVE Patented March 21, 1972 3,650,638

16 Sheets-Sheet 15 TABLE B3 VES CONDITION TRIPPED a .PRESSURIZED I 7 ZFP STROKE CONTROL *Tfi VALVE A TANKED VALVE m I POWER CIRCUIT VALVE ASSEMBLY CONTROL cmcun CONDITIONED FLOW ASSEMBLY 460 495 L Patented March 21, 1972 16 Sheets-Sheet 15 FIG.9C2

AFFECTED VALVES 2D 6 ZPR OPERATION OPENED CLOSED OPENED CLOSED VALVE CONDITION PRESSURIZED TANKED TANKED VALVE v wont OBJECTS AND SUMMARY OF THE INVEN- HYDRAULICALLY POWERED PUMP HAVING A PRECOMPRESSION FUNCTION to the power cylinders constituting the power end of the pumping unit. Thus, pulsation problems may also be created at the power end of the pump.

INDEX column It would, therefore, be highly desirable to provide a mul- ABSTRACT OF THE DISC LOSURE"; "31" T. tiplex pump which provides non-pulsating suction flow as well BACKGROUND OF THE INVENTION n 1 as discharge flow. It would also be desirable to operate such a pump with power fluid that flows into and out of the power TION 2 end ofthe pump without pulsation THE DRAWINGS 3 1 Another disadvantage the Previwsly P P P DETAILED DESCRIPTION U 4 E stems from the direct utilization of pressurized power fluid to General Summary 4 Prode the stroking of the P plunge"5 in each direction Detailed Structure '6 and in each cycle P Thus the cycle in each Pumping The Control valve Assembly n 6 is not inherently functionally dependent upon the cycle in the The Comm] valve Manifolds 8 h other unit. As a result, a phasing error in one stroke, e.g., over- The Precompression Valve. 10 travel uhdem'avel of the Power Plunger during P P The Power l id & C m Fl id Ci i u 2 sion, cannot be corrected without intervention by an operator Miscellaneous Valve Structures 13 so that the error y be self perpetuating A The Pumping Cycle 15 Furthermore, the previously proposed pumping unit does Th Automatic r k Control 22 not utilize the power fluid in the rod end of the power cylinder SUMMARY OF A 24 to a most efficient advantage. During discharge and precompression this fluid in the rod end may be exhausted to a power fluid reservoir where the potential power of this fluid, which is I pressurized by the rod displacement, is lost.

h lhvehhoh e to Pumps of the muhlplex type- More It would, therefore, be desirable to provide a multiplex particularly, this invention relates to a multiplex pump of the pump with a precompression function and a Semregulating: XP whlch the Pumped fluid precompressed Prior to stroke control, as well as with efficient utilization of power dlsehal'ge fluid in the rod end of the power cylinder.

In the oil industry it has been common in the past to utilize multiplex pumps designed to deliver pumped fluid at high OBJECTS AND SUMMARY OF THE INVENTION It is therefore, a general object of the invention to provide a pressures on the order of 15,000 psi. or greater. It has been found that even the slight compressibility of this relatively inmultiplex pump which obviates or minimizes disadvantages of the sort previously noted.

compressible pumped medium may result in a pulsating It is a particular object of the invention to provide an imdischarge pressure condition since a portion of the power in proved multiplex pump having a precompression function.

tended to accomplish the discharge phase of each pumping cycle is ihhel'ehtly utilized to first Compress the medium It is a further object of the invention to provide a multiplex; pump which provides non-pulsating suction flow as well as;

fore it is brought to discharge pressure.

This discharge pattern is particularly undesirable where discharge fl BACKGROUND OF THE INVENTION both high P p Pressure levels and y high delivery 40 It is another object of the invention to provide such a mulvolumes are involved. The resulting pulsations could, under tiplex pump hi may be fl id operated i h constant Such conditions, Subjeet the discharge conduits to Severe sure flow of power fluid into and out of the power end of thel vibrational forces. Thus, the pumping unit would be subject to Pump Stress conditions that might cause faihlte- It is a related object of the invention to provide a control;

It would, therefore be extremely desirable to Provide valve assembly for such a multiplex pump which establishes P p that is Capable of delivery of a high volume of fluid constant pressure and flow of power fluid into and out of the high pressure levels without being subject to pulsation power d f h Pump Pteblems- It is still another object of the invention to provide a mul-l To this end the present invention involves the provision of a ti l pump having a precompression f i d means f precompression function in the pump that continuously serves automatically regulating h pumping t k to bring p p fluid to a Pressure approaching discharge It is a related object of the invention to provide a multiplex pressure prior to actual discharge. Thus, a relatively smooth} pump h i a precompression fun tion and in which the constant Pressure Output of the P p fluid y be stroking in each pumping unit is responsive to the stroking in I tained. the other units.

It has been Previously Proposed Provide a fluid operated It is yet another object of the invention to provide an im-;

' discharge characteristics. This previously proposed pump is 1 tioned to undergo a discharge function while the other pumppumping cycle (i.e., suction, precompression and discharge) are not simultaneously performed, there is an absence of conduplex pump (operable on a highly compressible fluid) with a proved multiplex pump which may be fluid operated by the? precompression function in order to induce smoother use of separate power and control circuits.

A preferred embodiment of the invention intended to accomplish at least some of the foregoing objects comprises a multiplex pump having at least three pumping units each operable in a cycle including suction, precompression, and discharge phases, with the cycles of each unit being out of I phase with one another. The fluid end of the pump terminates in a common discharge line which is in fluid communication jwith the discharge end of each pumping unit. Likewise, the

suction ends of each of the pumping units are in communica 5 tion with a common suction line. stant pressure flow into the fluid end common to both pumpi O ti f h pump according to h d ib cycle i fluid operated in such a manner the one pumping unit is condiing unit undergoes both a suction and precompression function during the same time interval.

Although such a system may be satisfactory for some purposes, it may prove undesirable for a number of reasons.

For example, since all three functions associated with a l ing Chambefs- Therefore, the Suction line Suction h rl isures simultaneous performance of all functions associated common to the two pumping units is subject to pulsating flow;

I three functions also prevents constant pressure flow of power! iwith a given cycle to the end that constant pressure and flow that may have undesirable consequences similar to those inf h pumped fl id occurs i th ommon u tion line and in tended to be eliminated in connection with the discharge func-- the common discharge line.

tion. Each pumpingunit is fluid operated by power fluid acting Moreover, the lack of Simultaneous pe o a of l on a piston rod assembly extending between the fluid end and I a power cylinder assembly at the power end of that unit. Each fluid into and out of pressure and reservoir headers common' power li d bl i h t d through a ontrol alve assembly to a cornmon flow line communicating with a source of pressurized power fluid and a second common flow line communicating with a power fluid reservoir. By simultaneous performance of the suction, precompression and discharge. phases of the cycle, a substantially constant pressure flow of the power fluid to and from these common flow lines is provided.

The control valve assemblies each include two sleeve valves communicating with a common chamber, which in turn communicates with a power cylinder. When one sleeve valve of a given control valve assembly is in an open position and the other is closed, pressurized power fluid enters the associated power cylinder assembly to provide a discharge function in the fluid end of the associated fluid end cylinder assembly. When the sleeve valves are in a reversed position, a suction function is permitted resulting in discharge of the power fluid in the power cylinder assembly to the power fluid reservoir. During a phase of the cycle when both of these sleeve valves are in closed position, a precompression valve is opened, and power fluid is directed to the power cylinder through this precompression valve.

A separate control circuit is utilized to move the sleeve valves to their desired positions.

The rod ends of the power cylinders are fluid interconnected so that the functions in each pumping unit are performed in response to those'performed in the other units. Also, a portion of the power circuit is interrelated with the control circuit to provide for self-correction of the stroke lengths in the power cylinder assemblies.

THE DRAWINGS Other objects and advantages of the present invention will become apparent from the subsequent detailed description thereof in connection with the accompanying drawings in which:

FIG. 1 is a side elevational view partially broken away of a triplex pump according to the present invention;

FIG. 2 is a top plan view of the pump illustrated in FIG. 1;

FIG. 3 is a front elevational view of the pump shown in FIG. 1, illustrating the control valve assemblies associated with the power end of the pump and the interconnection of the control fluid manifold blocks;

FIG. 4 is a partial cross-sectional view of one control valve assembly;

FIG. 5 is a cross-sectional view of a precompression valve employed in the control valve assembly of FIG. 4;

FIG. 6 is an exploded perspective view of the lower control fluid manifold associated with the control valve assembly of FIG. 4;

FIG. 7 is an exploded perspective view of the upper control fluid manifold associated with the control valve assembly of FIG. 4;

FIG. 7A is a cross-sectional view of the upper portion of the control fluid manifold in FIG. 7 and the check valves assembled therein;

FIG. 8 is a schematic illustration of a power circuit and a control circuit of the present invention;

FIGS. 9A1, 981 and 9C1 are respectively schematic illustrations depicting the control valve conditions, the power circuit flow, and the power cylinder assembly functions respectively associated with the first, second and third phases of the pumping cycle;

TABLES A1, B1 and Cl respectively provide an index of the valve conditions and cylinder functions depicted in FIGS. 9A1, 981 and 9C1;

FIGS. 9A2, 9B2 and 9C2 schematically illustrate the positions of the control circuit conditioning valves, the resulting movement of the control valves, and the control circuit fluid flow that accomplishes this control valve movement in the phases of the pumping cycle respectively associated with FIGS. 9A1, 98] and 9C1;

TABLES A2, B2 and C2 provide an index of the condition of the control circuit conditioning valves and an index of the 4 control valve movement associated with these conditions as reflected in FIGS. 9A2, 982 and 9C2, respectively;

FIGS. 9A3, 983 and 9C3 schematically illustrate the tripping of the cycling valves and the resulting control circuit fluid flow that causes the positioning of the control circuit conditioning valves illustrated respectively in FIGS. 9A2, 982 and 9C2; and,

TABLES A3, B3 and C3 provide an index of the tripped valve and its affect on the control circuit conditioning valves as respectively illustrated in connection with FIGS. 9A3, 9B3 and 9C3.

DETAILED DESCRIPTION General Summary Referring now to FIGS. 1 and 2, an overall view of a triplex pump 20 according to the present invention is there shown.

The pump 20 includes a fluid end assembly 22 comprising three substantially identical cylinders 24. The fluid end assembly is of the type utilized in the I-IT'400 pump series referred to on page 6 of the "1968 Sales and Service Catalogue of Halliburton Services, Duncan, Oklahoma.

The internal passages 26 of each of the fluid end cylinders 24 are each in communication with a valved pump cylinder head 28 of the type more particularly described in U.S. Pat. No. 3,259,075, assigned to the assignee of the present invention. The disclosure of this patent is hereby incorporated by reference. Each of the cylinder heads 28 is provided with a conventional suction valve assembly 30 and a conventional discharge valve assembly 32. The discharge valve assemblies 32 communicate with a common discharge manifold 34, and the suction valve assembly similarly communicates with a common and conventional suction header (not shown). As will hereinafter become apparent (particularly with reference to US. Pat. No. 3,259,075) each ofthe discharge valve assemblies 32 is continuously available to yieldably resist fluid flow into the discharge manifold. The yieldable resistance, of

course, is operable during the hereinafter described precompression stages of a pumping cycle as well as during the discharge stages.

Extending from the fluid end assembly 22 in a direction away from the chambers 28 is a power end assembly 38. The ,power end assembly 38 includes three substantially identical power cylinders 40 having internal passages 41. Each of these 1 power cylinders 40 is in generally longitudinal alignment with one of the fluid end cylinders 24. A piston rod assembly 42 extends longitudinally into each power end cylinder 40 and the aligned fluid end cylinder 24. The ends of the piston rod assemblies 42 which extend into the chambers 26 of the fluid end cylinders 24 are provided by capped plunger ends, which function as pumping pistons 44 that are operable to bring about suction and discharge action in a conventional manner, and precompression action in a manner hereinafter more fully described.

The opposite ends, or power pistons, 46 of the piston rod assemblies 42 are in sliding and sealed engagement with the walls of the internal passages 41 of the power cylinders 40. In a manner hereinafter more fully described, power fluid acts on opposite faces 48 and 50 of the power pistons 46 to reciprocate the piston rod assemblies 42.

The power end assembly 38 and the fluid end assembly 22 are separated by a spacer frame assembly 51 which permits the fluid end piston rods, or plungers, 52 and the power end piston rods 54 to be separate members thereby facilitating maintenance operations. These rods 52 and 54 are each hollow, cylindrical members sealingly received in the fluid end cylinder passages 26 and the power end cylinder passages 41, as indicated at 55 and 56. If desired, a floating annular rod seal may be employed so as to allow the rods to operate slightly eccentric to the power cylinder bores, thereby eliminating the necessity of extremely accurate alignment between the power cylinders and the fluid end cylinders.

Extending longitudinally of and internally of each of these members are tie rods 57 which are joined at one end to the pistons 44 and 46 and at the opposite end with a cam actuator 58 to form, together with the rods 52 and 54 and their associated piston means 44 and 46, the integral piston rod as- .sembly 42. The permissible stroke length of each piston rod assembly 42 is such that each cam actuator 58 is movable between a back position adjacent the power end cylinders 40 and a forward position adjacent the fluid end cylinders 24.

In a manner hereinafter more fully described, the cam actuators 58 are operable, in connection with cycling valves FP, to provide a signal that the piston rod assembly has reached its forward position. These cycling valves FP are mounted on the spacer frame 51 at that forward position by suitable mounting means, indicated at 59. The location of this mounting means is such that the lengths of the cam actuator 58 cooperate with the valves FP for a time sufficient to permit the necessary circuit functions to take place.

In a similar manner, at least one cam actuator 58 is operable, in connection with a stroke control valve HP, to provide a signal that its associated piston rod assembly 42 has reached its back position. This stroke control valve BP is also mounted on the spacer frame 51 at that back position by suitable mounting means 60.

At the end of the power cylinders 40 remote from the fluid end assembly 22, each power cylinder is in continuous communication with one of three identical control valve assemblies CV. To facilitate description of a pump of the present invention, the three control valves are hereinafter referred to as l-CV, 2-CV and 3-CV, respectively. Similarly, the hereinafter ,described identical portions of the CV valve assemblies are differentiated by the prefixes 1-, 2- and 3-, as are the associated power cylinder assemblies 40.

The function of the control valves CV is to direct power fluid to and from the power cylinders 40 in a manner such that the power cylinders each operate on a suction, precompression, discharge cycle, each out of phase with one another.

In the discharge phase of the cycle in a given power cylinder 40, power fluid acts on the outer face 50 of a power piston 46 to transmit force through the piston rod 42 so as to cause the fluid end piston 44 to move to its forwardmost stroke position whereby fluid in the cylinder head 28 is expelled to the common discharge manifold 34. Prior to the discharge phase of the cycle, this fluid has been precompressed by power fluid acting on the power piston face 50 after passing through a precompression valve PR mounted on the control valve assembly CV. This precompression'flow of power fluid causes the power piston 46, through the piston rod assembly 42, to move forward by in increment sufficient to compress the fluid to be pumped and thereby raise the pressure ofthe fluid to approach the discharge pressure.

Suction movement of each power piston 46 is caused by power fluid acting on the inner face 48 of the power piston 46. The internal passages 41 of the power cylinders 40 are fluid interconnected in a normally closed circuit by a suitable common conduit 61. Thus fluid in two rod ends of the passages 41, which fluid is displaced during precompression and discharge movement of the associated power pistons 46, is caused to flow through this common conduit 61 into the third passage 41 to act on the inner face 48 of the power piston 46 in that third passage 41.

In this manner, the suction, precompression and discharge functions are simultaneously and responsively performed, one function being performed in each fluid end cylinder 24. Therefore, constant pressure flow continually exists between the fluid end of the pump and the common suction header and common discharge manifold 34.

For purposes of accomplishing automatic stroke correction, as hereinafter more fully described, the common conduit 61 connecting the rod ends of the power cylinders 40 is in fluid circuit with a conventional accumulator 62 and with a source of power fluid through a normally closed filling valve (not shown in FIG. 1) hereinafter described. Also, a rod end relief valve 222 provides selective communication between the rod ends and a power fluid reservoir.

Also, as hereinafter described, the control valve assemblies CV which direct the power fluid, preferably water, are, in the illustrated embodiment, monitored by a separate control fluid circuit, preferably utilizing a different fluid such as oil, air or a combination thereof. It will, however, be apparent that conr651 limited distance, during reciprocation of the piston rod assemblies 42, so as to relieve stresses on those members. Provision for such movement may be made by supporting the members 65 providing the connection between the spacer frame 51 and the cylinders 40 and 24 for limited sliding movement within suitable brackets as indicated at 66 and 68. These connecting members 65 may, in turn, be joined by tie bars 69. Detailed Structure The Control Valve Assembly Referring now particularly to FIGS. 3 and 4, the previously identified identical control valve assemblies 1CV, 2CV and 3CV will be described.

From the partial cross sectional view of one assembly shown in FIG. 4, it may be seen that each assembly includes two pilot operated sleeve valves, I and D, which respectively provide for the inlet of power fluid to an associated power cylinder 40 and the discharge of power fluid from that cylinder. The sleeve valves I and D are generally vertically aligned and are slidably received in vertically aligned cylinders 70 and 72.

The bottom of the lower cylinder 70 communicates with a power fluid inlet elbow 74. Internally each elbow 74 is provided with a stepped bore indicated at 76, which continuously communicates with a source of pressurized power fluid. Referring to FIG. 3, it will be seen that the inlet elbows 74 of the control valve 1CV, 2CV and 3CV communicate with a common passageway 75 which is turn provides the continuous fluid communication with pressurized power fluid.

The smaller internal diameter of the inlet elbow 74 at the step 76 is less than the external diameter of the lower end of the lower sleeve I so that downward movement of this sleeve beyond the step is prevented.

The upper end of the lower cylinder 70 and the lower end of the upper cylinder 72 are spaced from one another and are joined to a common, generally cylindrical, housing 78. This housing 78 is provided with a laterally facing opening 80 communicating with the piston end of a power cylinder 40 (see FIG. 1) and with a central chamber 82 within the housing. Within the chamber 82 is a slotted spacer 84 which is generally cylindrical and has an internal bore generally aligned with the lower cylinder 70.

This spacer 84 is provided, adjacent its lower end, with lateral slots 86 communicating with the central chamber 82. On top of the spacer and blocking its central bore from vertical communication with the central chamber 82 is a soft seat 88. The relationship of the outer diameter of the upper portion of the lower sleeve I and the inner diameter of the spacer 84 is such that when the lower sleeve I is in its uppermost position abutting the soft seat 88, fluid communication between the chamber 82 and the inlet elbow 74 is totally blocked. However, when the lower sleeve I is in its lowermost position adjacent the elbow shelf 76, fluid communication between the elbow inlet 74 and the chamber 82 is established by means of the lateral slots 86 and the sleeve valve I.

The upper end of the control valve assembly is surrounded by a cylindrical discharge housing 90 defining a discharge chamber 92. The discharge chambers 92 of the control valve assemblies are in communication with one another and in continuous communication with a power fluid reservoir by means of connecting conduits 93 (FIG. 3) and (93', the former of which may by flexible to permit relative movement of the con- 

1. A multiplex pump comprising: at least three pumping units; each of said pumping units having a fluid end in valved communication with a common suction conduit means and in continuous yieldable valved communication with a common discharge conduit means; and power means for simultaneously operating each of said pumping units in a cycle including distinct suction, precompression and discharge stages, with simultaneous performance of different ones of said stages in different ones of said pumping units providing substantially constant pressure and flow in said common suction conduit means and said common discharge conduit means; said power means controlling said precompression stages remote from said fluid ends.
 2. control circuit pump means for selectively delivering opening actuator control fluid to said opening actuator chambers of said inlet and discharge valve means so as to place said inlet and discharge valve means in their said selective fluid communication positions, and
 2. A multiplex pump according to claim 1 wherein said power means comprises: fluid power means; and a power end assembly defining a power end of each of said pumping units in valved communication with a common pressurized hydraulic fluid conduit means providing a source of pressurized hydraulic power fluid of said fluid power means a common reservoir conduit means communicating with an hydraulic power fluid reservoir of said fluid power means; and wherein: the simultaneous performance of said different ones of said cycle stages in different ones of said pumping units provides substantially constant pressure flow in said common pressurized fluid conduit means and said common reservoir conduit means.
 2. power fluid pump means for delivering pressurized power fluid from said power fluid reservoir means,
 3. flow regulating means operatively connecting the pressurized fluid delivered by said pump means to said plurality of piston and cylinder assemblies and to said reservoir means, said flow regulating means including: a. a plurality of power circuit valve means, each for selectively placing one of said piston and cylinder pumping assemblies in generally unrestricted fluid communication with said pressurized power fluid, in relatively restricted fluid communication with a reduced flow of said pressurized power fluid, or in fluid communication with said fluid reservoir means, b. each of said power circuit valve means comprising: i. power fluid inlet valve means having power fluid entry and exit passages, ii. power fluid discharge valve means having power fluid entry and exit passages, and iii. precompression valve means having a power fluid entry port, a power fluid output port having restricted passage, a power fluid pilot port, and means normally blocking said entry port from said output port when pilot pressure exists in said pilot port, iv. said entry passage of said inlet valve means and said entry port of said precompression valve means being in continuous communication with pressurized power fluid delivered by said power fluid pump means, v. a common chamber selectively in fluid communication with said exit passage of inlet valve means, and in continuous fluid communication with one of said rod ends of said pumping assemblies, with said output port of said precompression valve means, and with said inlet passage of said discharge valve means, vi. said outlet passage of said discharge valve means being in selective fluid communication with said power fluid reservoir means, vii. said pilot ports of each of said precompression valve means being in continuous communication with one of said output ports of another one of said precompression valve means.
 3. A multiplex pump according to claim 2 wherein each of said power end assemblies includes a power cylinder assembly receiving a power piston rod assembly, said power means further including: rod end common conduit means for interconnecting the rod ends of said power cylinder assemblies in normally closed hydraulic power fluid circuit for responsive stroking operation of said power piston and piston rod assemblies.
 3. control circuit reservoir means for draining control circuit fluid from selected ones of said opening actuator chambers upon movement of selected ones of said inlet and discharge valve means to their noncommunicating positions.
 4. A multiplex pump according to claim 3 wherein said fluid power means further comprises: stroke correction means for automatically regulating the amount of hydraulic power fluid in said normally closed fluid circuit of said rod ends in response to stroking errors.
 5. A multiplex pump according to claim 2 wherein said power means further includes: control valve means for selectively providing said valved communication between each said power end of each said pumping unit with said common pressurized fluid conduit means and said common reservoir conduit means; and precompression valve means for selectively providing valved communication between each said power end of each said pumping unit with said common pressurized fluid conduit means.
 6. A multiplex pump according to claim 5 further including: control fluid circuit means for conditioning said control valve means so as to insure continuous maintenance of conditioned communication between at least one of said power ends and said common pressurized fluid conduit means, and conditioned communication between at least a second of said power ends and said common reservoir conduit means; and wherein: at least a third one of said power ends is in communication with said common pressurized fluid conduit means through said precompression valve means during said conditioned communication.
 7. A multiplex pump comprising: at least three pumping units each having a fluid end communicating with a common suction conduit means and communicating through yieldable valve means with a common discharge conduit means; each of said pumping units being operable in a cycle including suction, precompression and discharge stages, the cycles being out of phase witH one another; and means remote from said fluid end for controlling said stages.
 8. A multiplex pump comprising: at least three pumping chambers each having a fluid end communicating with a common suction conduit means and a common discharge conduit means, at least three yieldable fluid end discharge valve means, each being operably associated with one of said at least three pumping chambers and said common discharge conduit means, and each being operable to yieldably resist fluid flow from the associated one of said pumping chambers into said discharge conduit means; at least three pumping means, each being operably associated with one of said at least three pumping chambers and comprising: suction means for drawing fluid into its associated chamber from said common suction conduit means, precompression means for precompressing said fluid in its associated chamber, and discharge means for expelling said precompressed fluid from its associated chamber through the associated one of said yieldable fluid end discharge valve means and into said common discharge conduit means; and means for operating each of said at least three pumping means in a cycle including distinct suction, precompression and discharge stages with the cycles of each of said at least three pumping means being out of phase with one another.
 9. In a multiplex pump of the type having at least three pumping chambers each having a fluid end communicating with a suction flow source and communicating with a common discharge flow conduit through an associated yieldable fluid end discharge valve means operable to yieldably resist fluid flow into said common discharge flow conduit, the improvement comprising: at least three suction means, each for respectively drawing fluid from said common suction flow source into one of said at least three pumping chambers; at least three precompression means, each for respectively precompressing, at a controlled rate, said fluid drawn into one of said pumping chambers by operation of one of said suction means; at least three discharge means, each for respectively pumping the precompressed fluid out of one of said pumping chambers through an associated yieldable fluid end discharge valve means and into said common discharge flow conduit; and control means for operating each of the sets of said ones of said suction means, said precompression means and said discharge means associated with the same one of said pumping chambers in a cycle including distinct suction precompression and discharge stages, with the sets of said suction means, said precompression means and said discharge means associated with each of said at least three pumping chambers being cyclically operable out of phase with the other ones of said sets; said control means controlling said precompression stages remote from said fluid ends.
 10. A fluid operated multiplex pump comprising: at least three pumping units, each operable in a cycle including suction, precompression and discharge stages; said pumping units including power end assemblies comprised of power cylinder assemblies receiving power piston and piston rod assemblies defining power ends and rod ends; said rod ends being interconnected in a normally closed hydraulic fluid circuit; power fluid circuit means for providing flow of hydraulic power fluid to and from said power ends to cyclically operate said pumping units; rod end correction circuit means for withdrawing and adding fluid to said normally closed rod end fluid circuit in response to pumping errors in said suction, precompression and discharge stages; and control circuit means for conditioning said power fluid circuit means for cyclically operating said pumping units, and for conditioning said rod end correction circuit means to normally maintain a fixed amount of fluid in said interconnected rod ends.
 11. A fluid operated triplex pump comprising: A. three piston and cylinDer pumping assemblies, each operable in a suction, precompression and discharge cycle out of phase with one another; B. each of said piston and cylinder assemblies including a power end and a fluid end, and a rod end; C. hydraulic power fluid circuit means for cyclically operating each of said piston and cylinder pumping assemblies in said suction, precompression and discharge cycle; and D. control circuit means for conditioning said power circuit means to cycle said piston and cylinder pumping assemblies; E. said power fluid circuit means comprising:
 12. A fluid operated triplex pump according to claim 11 wherein said control circuit means comprises control fluid circuit means including:
 13. A multiplex pump according to claim 12 including: means for supplying control circuit fluid to said opening actuator chambers of said discharge valve means in two stages.
 14. An hydraulically powered multiplex pump comprising: at least three pumping chambers each having a fluid end communicating with a common suction conduit means and a common discharge conduit means, at least three yieldable fluid end discharge valve means, each being operably associated with one of said at least three pumping chambers and said common discharge conduit means, and each being operable to yieldably resist fluid flow from the associated one of said pumping chambers into said discharge conduit means; at least three hydraulic fluid powered pumping means, each being operably associated with one of said at least three pumping chambers and comprising: suction means for drawing fluid into its associated chamber from said common suction conduit means, precompression means for precompressing said fluid in its associated chamber, and discharge means for expelling said precompressed fluid from its associated chamber through the associated one of said yieldable fluid end discharge valve means and into said common discharge conduit means, and hydraulic power fluid circuit means for operating each of said at least three hydraulic fluid powered pumping means in a cycle including distinct suction, precompression and discharge stages with the cycles of each of said at least three pumping means being out of phase with one another; said hydraulic power fluid circuit means including means for controlling the rate of precompression by said precompression means remote from said fluid end.
 15. An hydraulically powered multiplex pump comprising: at least three piston and cylinder pumping assemblies; each of said piston and cylinder pumping assemblies including a power end assembly and a fluid end assembly; each of said fluid end assemblies being in communication with a common suction conduit and being in valved communication with a common discharge conduit; at least three yieldable fluid end discharge valve means, each providing said valved communication with said discharge conduit by yieldably resisting the flow of fluid from one of said fluid end assemblies to said discharge conduit; hydraulic power fluid circuit means for cyclically operating each of said piston and cylinder pumping assemblies in a cycle including suction, precompression and discharge stages, with the cycles being out of phase with one another, said hydraulic power fluid circuit means including: power fluid pump means for providing a source of pressurized hydraulic power fluid, power circuit valve means for providing discharge flow of said power fluid to said power end assemblies and for providing suction flow of hydraulic power fluid from said power ends, and precompression valve means for providing precompression flow of said power fluid to said power end assemblies to causing extension of said pistons, at a rate controlled remote from said fluid end to precompress fluid in said fluid ends while discharge of the fluid being precompressed is resisted by said yieldable fluid end discharge valve means.
 16. An hydraulically powered multiplex pump according to claim 15 including: control fluid circuit means for controlling operation of said power circuit valve means and said precompression valve means.
 17. An hydraulically powered multiplex pump according to claim 15 wherein: said power circuit valve means provide communication between each of said power end assemblies and both a common pressurized power fluid conduit means and a common power fluid reservoir conduit means.
 18. An hydraulically powered multiplex pump according to claim 15 wherein: said power end assemblies includes rod ends interconnected in normally closed hydraulic power fluid circuit for responsive stroking of said pistons.
 19. An hydraulically powered multiplex pump according to claim 16 including: stroke correction means for automatically regulating the amount of hydraulic power fluid in said normally closed circuit in response to stroking errors.
 20. An hydraulically powered multiplex pump comprising: at least three piston and cylinder pumping assemblies; each of said piston and cylinder pumping assemblies including a power eNd assembly and a fluid end assembly; each of said power end assemblies including a rod end; hydraulic power fluid means for cyclically operating each of said piston and cylinder pumping assemblies in a cycle including suction, precompression and discharge stage, with the cycles being out of phase with one another; and rod end common conduit means interconnecting said rod ends in normally closed hydraulic power fluid circuit for responsive stroking of said pistons.
 21. An hydraulically powered multiplex pump according to claim 20 including: stroke correction means for automatically regulating the amount of hydraulic power fluid in said normally closed circuit in response to stroking errors. 